Psttm device with free magnetic layers coupled through a metal layer having high temperature stability

ABSTRACT

MTJ material stacks, pSTTM devices employing such stacks, and computing platforms employing such STTM devices. In some embodiments, perpendicular MTJ material stacks with free magnetic layers are magnetically coupled through a metal material layer for improved stability and low damping. In some advantageous embodiments, layers of a free magnetic material stack are magnetically coupled through a coupling layer of a metal comprising at least molybdenum (Mo). The Mo may be in pure form or alloyed with other constituents.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application contains subject matter related to PCT ApplicationUS15/______, (Docket No. 01.P87085PCT), titled “PSTTM DEVICE WITHMULTI-LAYERED FILTER STACK” filed on Sep. 25, 2015, and PCT ApplicationUS15/______, (Docket No. 01.P87086PCT), titled “PSTTM DEVICE WITH BOTTOMELECTRODE INTERFACE MATERIAL” filed on Sep. 25, 2015.

BACKGROUND

STTM devices are non-volatile memory devices that utilize a phenomenonknown as tunneling magnetoresistance (TMR). For a structure includingtwo ferromagnetic layers separated by a thin insulating tunnel layer, itis more likely that electrons will tunnel through the tunnel layer whenmagnetizations of the two magnetic layers are in a parallel orientationthan if they are not (non-parallel or antiparallel orientation). Assuch, a magnetic tunneling junction (MTJ), typically comprising a fixedmagnetic layer and a free magnetic layer separated by a tunnelingbarrier layer, can be switched between two states of electricalresistance, one state having a low resistance and one state with a highresistance. The greater the differential in resistance, the higher theTMR ratio: (R_(AP)−R_(p))/R_(p)*100% where R_(p) and R_(AP) areresistances for parallel and antiparallel alignment of themagnetizations, respectively. The higher the TMR ratio, the more readilya bit can be reliably stored in association with the MTJ resistivestate. The TMR ratio of a given MTJ is therefore an importantperformance metric of an STTM.

For an STTM device, current-induced magnetization switching may be usedto set the bit states. Polarization states of one ferromagnetic layercan be switched relative to a fixed polarization of the secondferromagnetic layer via the spin transfer torque phenomenon, enablingstates of the MTJ to be set by application of current. Angular momentum(spin) of the electrons may be polarized through one or more structuresand techniques (e.g., direct current, spin-hall effect, etc.). Thesespin-polarized electrons can transfer their spin angular momentum to themagnetization of the free layer and cause it to precess. As such, themagnetization of the free magnetic layer can be switched by a pulse ofcurrent (e.g., in about 1-10 nanoseconds) exceeding a certain criticalvalue, while magnetization of the fixed magnetic layer remains unchangedas long as the current pulse is below some higher threshold associatedwith the fixed layer architecture.

MTJs with magnetic electrodes having a perpendicular (out of plane ofsubstrate) magnetic easy axis have a potential for realizing higherdensity memory than in-plane variants. Generally, perpendicular magneticanisotropy (PMA) can be achieved in the free magnetic layer throughinterfacial perpendicular anisotropy established by an adjacent layer,such as magnesium oxide (MgO), when the free magnetic layer issufficiently thin. A thin free magnetic layer however is associated withgreater instability, which can significantly shorten the non-volatilelifetime of a memory element. Stability is one of the most importantissues facing the scaling of STTM based devices and memory arraysfabricated there from.

BRIEF DESCRIPTION OF THE DRAWINGS

The material described herein is illustrated by way of example and notby way of limitation in the accompanying figures. For simplicity andclarity of illustration, elements illustrated in the figures are notnecessarily drawn to scale. For example, the dimensions of some elementsmay be exaggerated relative to other elements for clarity. Further,where considered appropriate, reference labels have been repeated amongthe figures to indicate corresponding or analogous elements. In thefigures:

FIG. 1 is a cross-sectional view of a material layer stack for a pSTTMdevice, in accordance with some embodiments of the present invention;

FIG. 2 is a graph of anisotropy field as a function of a magneticmaterial layer thickness over two different underlayer materials, inaccordance with some embodiments;

FIG. 3 is a graph of damping as a function of a magnetic material layerthickness over two different underlayer materials, in accordance withsome embodiments;

FIG. 4 is a bar chart comparing MTJ performance parameters for twodifferent coupling material layers, in accordance with some embodiments;

FIG. 5A is a cross-sectional view of a material layer stack for a pSTTMdevice further including a multi-layered filter stack, in accordancewith some further embodiments of the present invention;

FIG. 5B is a cross-sectional view of a material layer stack for a pSTTMdevice further including an electrode interface material layer/stack, inaccordance with some further embodiments of the present invention;

FIG. 6 is a flow diagram illustrating a method of fabricating the STTMdevice illustrated in FIG. 1 or FIG. 2, in accordance with someembodiments;

FIG. 7 is a schematic of a STTM bit cell, which includes a spin transfertorque element, in accordance with an embodiment of the presentinvention;

FIG. 8 is a schematic illustrating a mobile computing platform and adata server machine employing STTM arrays, in accordance withembodiments of the present invention; and

FIG. 9 is a functional block diagram illustrating an electroniccomputing device, in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

One or more embodiments are described with reference to the enclosedfigures. While specific configurations and arrangements are depicted anddiscussed in detail, it should be understood that this is done forillustrative purposes only. Persons skilled in the relevant art willrecognize that other configurations and arrangements are possiblewithout departing from the spirit and scope of the description. It willbe apparent to those skilled in the relevant art that techniques and/orarrangements described herein may be employed in a variety of othersystems and applications other than what is described in detail herein.

Reference is made in the following detailed description to theaccompanying drawings, which form a part hereof and illustrate exemplaryembodiments. Further, it is to be understood that other embodiments maybe utilized and structural and/or logical changes may be made withoutdeparting from the scope of claimed subject matter. It should also benoted that directions and references, for example, up, down, top,bottom, and so on, may be used merely to facilitate the description offeatures in the drawings. Therefore, the following detailed descriptionis not to be taken in a limiting sense and the scope of claimed subjectmatter is defined solely by the appended claims and their equivalents.

In the following description, numerous details are set forth. However,it will be apparent to one skilled in the art, that the presentinvention may be practiced without these specific details. In someinstances, well-known methods and devices are shown in block diagramform, rather than in detail, to avoid obscuring the present invention.Reference throughout this specification to “an embodiment” or “oneembodiment” means that a particular feature, structure, function, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. Thus, the appearances ofthe phrase “in an embodiment” or “in one embodiment” in various placesthroughout this specification are not necessarily referring to the sameembodiment of the invention. Furthermore, the particular features,structures, functions, or characteristics may be combined in anysuitable manner in one or more embodiments. For example, a firstembodiment may be combined with a second embodiment anywhere theparticular features, structures, functions, or characteristicsassociated with the two embodiments are not mutually exclusive.

As used in the description of the invention and the appended claims, thesingular forms “a”, “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willalso be understood that the term “and/or” as used herein refers to andencompasses any and all possible combinations of one or more of theassociated listed items.

The terms “coupled” and “connected,” along with their derivatives, maybe used herein to describe functional or structural relationshipsbetween components. It should be understood that these terms are notintended as synonyms for each other. Rather, in particular embodiments,“connected” may be used to indicate that two or more elements are indirect physical, optical, or electrical contact with each other.“Coupled” may be used to indicated that two or more elements are ineither direct or indirect (with other intervening elements between them)physical or electrical contact with each other, and/or that the two ormore elements co-operate or interact with each other (e.g., as in acause an effect relationship).

The terms “over,” “under,” “between,” and “on” as used herein refer to arelative position of one component or material with respect to othercomponents or materials where such physical relationships arenoteworthy. For example in the context of materials, one material ormaterial disposed over or under another may be directly in contact ormay have one or more intervening materials. Moreover, one materialdisposed between two materials or materials may be directly in contactwith the two layers or may have one or more intervening layers. Incontrast, a first material or material “on” a second material ormaterial is in direct contact with that second material/material.Similar distinctions are to be made in the context of componentassemblies.

As used throughout this description, and in the claims, a list of itemsjoined by the term “at least one of” or “one or more of” can mean anycombination of the listed terms. For example, the phrase “at least oneof A, B or C” can mean A; B; C; A and B; A and C; B and C; or A, B andC.

Described herein are MTJ material stacks, STTM devices employing suchmaterial stacks, and computing platforms employing such STTM devices. Insome embodiments, perpendicular MTJ material stacks include freemagnetic layers magnetically coupled through a metal material layer forimproved stability and low damping. Applications for embodimentsdescribed herein include embedded memory, embedded non-volatile memory(NVM), magnetic random access memory (MRAM), and non-embedded orstand-alone memories.

Thermal stability Δ is one of the most important issues facing scalingof STTM based devices and memory arrays fabricated there from. Greaterthermal stability is associated with longer memory element non-volatilelifetimes. As scaling continues, it becomes more difficult to maintainsufficient stability. Thermal stability is defined as the energy barrierE between two magnetic states (e.g., (1, 0), (parallel, anti-parallel)).Stability is equal to the product of magnetic anisotropy k_(eff) of thefree magnetic material and volume of free magnetic material (thickness tmultiplied by material stack area A) divided by thermal energy (k_(B)T):

$\begin{matrix}{\Delta = {\frac{\kappa_{eff}{tA}}{k_{B}T}.}} & (1)\end{matrix}$

Generally, a stability value of at least 60 k_(B)T is considered asuitable for most applications. However, it is clear that scaling of amemory cell area reduces stability and the 60 k_(B)T target becomesharder to achieve. Magnetic anisotropy is further a function ofsaturation magnetization M_(s) and effective anisotropy field H_(k,eff)such that thermal stability may be improved through an increase inanisotropy field. Perpendicular magnetic anisotropy (PMA) in the freemagnetic layer can achieve greater H_(k,eff) in the presence ofinterfacial perpendicular anisotropy established by an adjacent layer,such as magnesium oxide (MgO), when the free magnetic layer issufficiently thin.

Damping relates to a magnetic friction that a spin's magnetizationexperiences as the spin switches from one state to another. Greaterdamping means that a larger critical write current J_(c) is needed toswitch the magnetization of the free layer from one state to another.Critical current J_(c) is proportional to a damping constant αmultiplied by a ratio of stability over spin transfer efficiency (˜TMR).Damping increases however as free magnetic layer thickness decreases dueto spin pumping effect. Often then, increases in anisotropy alsoincrease the critical current density linearly, making it difficult toachieve higher stability without a concomitant increase in damping.

In some embodiments, the stability of an STTM cell is enhanced alongwith providing reduced damping through incorporation of a plurality offree magnetic layers within the stack that are coupled through acoupling material having tolerance to high temperature processing. FIG.1 is a cross-sectional view of a MTJ material stack 101 for aperpendicular STTM device, in accordance with some embodiments of thepresent invention.

MTJ material stack 101 includes a first metal electrode 107 (e.g.,bottom electrode) disposed over a substrate 105. A fixed magneticmaterial layer or stack 120 including one or more layer of magneticmaterial is disposed over electrode 107. A tunneling dielectric materiallayer 130 (e.g., MgO, MgAlO) is disposed over fixed magnetic materiallayer or stack 120. A free magnetic material layer stack 155 is disposedover tunneling dielectric material layer 130. Free magnetic materialstack 155 includes a plurality of free magnetic material layersmagnetically coupled through an intervening metal coupling materiallayer. In the exemplary embodiment a metal coupling material layer 150is disposed between a first free magnetic material layer 140 and asecond free magnetic material layer 160. In the exemplary embodimentillustrated, a dielectric material layer 170, such as a metal oxide(e.g., MgO, VO, WO, TaO, HfO, MoO), is disposed over free magneticmaterial stack 155. Such a capping layer may be absent for spin-halleffect (SHE) implementations. A second metal electrode 180 (e.g., topelectrode) is disposed over the capping dielectric material layer 170.Notably, the order of the material layers 107-180 may be inverted, orextending laterally away from a topographic feature sidewall, inalternative embodiments.

In some embodiments, the material stack shown in FIG. 1 is aperpendicular system, where spins of the magnetic layers areperpendicular to the plane of the material layers (i.e., the magneticeasy axis is in the z-direction out of the plane of substrate 105).Fixed magnetic layer 120 may be composed of any material or stack ofmaterials suitable for maintaining a fixed magnetization direction whilethe free magnetic material stack 155 is magnetically softer (i.e.magnetization can easily rotate to parallel and antiparallel state withrespect to fixed layer). In some embodiments, MTJ structure 101 is basedon a CoFeB/MgO system, having an MgO tunneling material layer 130, CoFeBfixed magnetic layer/stack 120, and CoFeB free magnetic layers 140, 160.In advantageous embodiments, all CoFeB layers have body-centered cubic(BCC) (001) out-of-plane texture, where texture refers to thedistribution of crystallographic orientations within in the layers ofMTJ structure 101. For at least some such embodiments, a high percentageof CoFeB crystals have the preferred (001) out-of-plane orientation(i.e., the degree of texture is high). In some embodiments, the (001)oriented CoFeB magnetic material layers 120, 140, and 160 are iron-richalloys (i.e., Fe>Co) for increased magnetic perpendicularity. In someembodiments, Fe content is at least 50%. Exemplary embodiments include20-30% B (e.g., Co₂₀Fe₆₀B₂₀). Other embodiments with equal parts cobaltand iron are also possible (e.g., Co₄₀Fe₄₀B₂₀). Other magnetic materialcompositions are also possible for the fixed and/or free magneticlayers, such as but not limited to: Co, Fe, Ni, and non-boron alloys ofthese metals (e.g., CoFe). In some advantageous embodiments, filmthickness of free magnetic layer 140 is 0.6-1.6 nm, while film thicknessof free magnetic layer 160 is 0.1-1 nm. Free magnetic layer 140 may bethicker than free magnetic layer 160 to compensate any remaining deadregion. In some embodiments however, free magnetic layers 140 and 160have equal thickness as Mo coupling layers have been found to improveperformance in a manner that suggest reduced dead layer thicknesses.

Tunneling dielectric material layer 130 is composed of a material orstack of materials suitable for allowing current of a majority spin topass through the layer, while impeding current of a minority spin (i.e.,a spin filter), impacting the tunneling magnetoresistance associatedwith MTJ material stack 101. In some exemplary embodiments, dielectricmaterial layer 130 is magnesium oxide (MgO). Dielectric material layer130 may further provide a crystallization template (e.g., BCC with (001)texture) for solid phase epitaxy of free magnetic material stack 155and/or fixed magnetic material layer or stack 120.

In some embodiments, layers of a free magnetic material stack aremagnetically coupled through a metal coupling layer having hightemperature (HT) tolerance. As employed herein, high temperaturetolerance of the metal coupling layer is in reference to the ability ofthe coupling material to maintain desirable free magnetic layercharacteristics, (e.g., high stability Δ and high anisotropy k_(eff))through subsequent thermal treatments associated with integrated circuitdevice fabrication. Notably, a vacuum thermal anneal (e.g., ˜250-300°C.) is typically performed to allow magnetic materials reach a desirablecrystallinity and texture from substantially amorphous as-depositedstate. However, many processes conventional to MOS transistor integratedcircuitry (IC) fabrication are performed at 400° C. The inventors havefound that many free magnetic material stacks incorporating a couplingmaterial layer suffer significant degradation in K_(eff) as thermaltreatments exceed 300° C., rendering such a MTJ material stack difficultto integrate with MOS transistor IC fabrication.

In some advantageous embodiments, layers of a free magnetic materialstack are magnetically coupled through a coupling layer of a metalcomprising at least molybdenum (Mo). The Mo may be in pure form oralloyed with other constituents. In advantageous embodiments, the metalcoupling material layer is at least predominantly Mo (e.g., Mo is theconstituent of greatest proportion in the coupling material). In someexemplary embodiments, the coupling material is elemental Mo (i.e., noother intentional constituents). In alloyed Mo embodiments, the alloyconstituents may be substantially absent from the free magneticmaterials, or may also be present in the free magnetic materials. Inadvantageous alloyed Mo embodiments, the Mo alloy has a dominant stableBCC phase. In some exemplary embodiments Mo is alloyed one or more ofTa, W, Nb, V, Hf and Cr. The thickness of the coupling material layerhas also been found to be important, advantageously being just a fewangstroms to minimize damping. In some embodiments of a Mo couplinglayer, the Mo film has a thickness less than 1 nm, and advantageously0.1 and 0.8 nm.

The inventors have found Mo superior to various other metal couplingmaterials (e.g., Tungsten (W), Tantalum (Ta)). Experiments performedwith exemplary stacks based on CoFeB/MgO/CoFeB indicate Mo provides asignificant improvement in both stability and damping relative to W.FIG. 2 is a graph of anisotropy field as a function of a magneticmaterial layer thickness over a W underlayer and a (pure) Mo underlayer,in accordance with some embodiments. The illustrated measurements werecollected from samples prepared as a partial MTJ stack including a layerof CoFeB (CFB) having a reference composition and of varying thicknessesdisposed on a layer of MgO over a silicon dioxide substrate layer. Priorto measurement, the partial stacks were annealed at a temperature of400° C. for 30 min to simulate subsequent high temperature processing.In FIG. 2, positive values of H_(k,eff) are associated with greater PMA,and therefore advantageous. For at least the thickness range where adirect comparison is made (e.g., 1.2-2.0 nm), the Mo underlayer displaysmore positive (higher) H_(k,eff). A Mo underlayer also demonstratedlower damping constant. FIG. 3 is a graph of damping as a function of aCoFeB magnetic material layer thickness for the W underlayer and Mounderlayer, in accordance with some embodiments. The illustratedmeasurements were again collected from samples prepared as a partial MTJstack including a layer of CoFeB having a reference composition and ofvarying thicknesses disposed on a layer of MgO over a silicon dioxidesubstrate layer. As illustrated, damping constant α decreases withincreasing CoFeB thickness, as expected. Over the range of magneticmaterial thicknesses, Mo displays significantly lower damping than W.Lower damping will advantageously reduce the critical current densityfor the same stability device. FIG. 4 is a bar chart comparing MTJparameters for W and Mo coupling materials in a free magnetic materialstack, in accordance with some embodiments. The illustrated measurementswere collected from full MTJ stack including a layer of CoFeB having areference composition and thickness disposed on a first layer of MgO andcapped with a second layer of MgO. As shown, relative to a W couplinglayer the free magnetic material stack including the Mo coupling layerhas lower damping and higher K_(eff)*t (i.e., high stability) while TMRof the stacks are essentially identical.

A good coupling material is to magnetically couple together the freemagnetic material layers directly contacting the coupling material layersuch that the coupling material layer increases the effective magneticthickness of the free magnetic layer, and thereby improves thermalstability of the MTJ for a same given stack area. The coupling materiallayer has many functions and may have an important role in a variety ofphysical mechanisms that can impact a MTJ material stack. Filmcomposition and the attendant crystallographic and interface propertiesmay impact, for example, magnetic coupling strength of the insertionmaterial, as well as solid phase epitaxy of the free magnetic layers.Interactions of these parameters introduce complexity in architecting afree magnetic material stack having tolerance to high temperature (e.g.,400° C.) processing. Mo has BCC crystal structure in the most stablephase, which is advantageous for promoting magnetic perpendicularity infree magnetic layers such as CoFeB. The coupling material (anddeposition of the coupling layer) might also have a significant role inthe formation of magnetic dead zones during high temperature processing,particularly within the free magnetic material layer upon which thecoupling material layer is deposited. Although not bound by theory, onepossible explanation for the improvement in damping observed for the Mocoupling layer in FIG. 3 is a reduction in magnetic dead zones in theunderlying CoFeB free magnetic material, which would increase theeffective thickness of the free magnetic material. Although not bound bytheory, a reduction in the magnetic dead zone may be attributable to alower atomic mixing of the underlying free magnetic material. Mo has amuch lower atomic number (Z) than W, for example, and as such may bedeposited onto the free magnetic material with lower energy. Thecoupling material layer may also getter dopants from the free magneticlayers (e.g., getter B from CoFeB), which is currently thought toimprove the crystallization of the free magnetic layers and therebyimprove stability and/or magnetic anisotropy. Low rates of diffusion forthe coupling material into the free magnetic material layers may also beimportant.

In further reference to FIG. 1, it is noted an MTJ stack may varyconsiderably below tunneling layer 130 without deviating from the scopeof the embodiments of the present invention. For example, one or moreintermediate layer may be disposed between the fixed magnetic materiallayer 120 and adjacent contact metallization 107. In some embodiments,an anti-ferromagnetic layer, such as, but not limited to, iridiummanganese (IrMn) or platinum manganese (PtMn), or a syntheticantiferromagnetic (SAF) structure may be incorporated into an MTJ stackthat includes free magnetic material stack 155. SAF structures may beuseful for countering a fringing magnetic field associated with fixedmagnetic material layer 120. Such additional material layers may beconsidered part of a multi-layered fixed magnetic material stack.

FIG. 5A is a cross-sectional view of a material layer stack for a pSTTMdevice 501 further including a multi-layered filter stack, in accordancewith some further embodiments of the present invention. The materialstack includes a SAF stack 505 disposed over metal electrode 107.Although not depicted, one or more material layers may be disposedbetween SAF stack 505 and metal electrode 107 and/or metal electrode 107may comprise a plurality of material layers. In some exemplaryembodiments, SAF stack 505 includes a first plurality of bilayers 113forming a superlattice of ferromagnetic material (e.g., Co, CoFe, Ni)and a nonmagnetic material (e.g., Pd, Pt, Ru). Bi-layers 113 may includen bi-layers (e.g., n [Co/Pt] bilayers, or n [CoFe/Pd] bilayers, etc.)that are separated from a second plurality of bilayers 115 (e.g., p[Co/Pt]) by an intervening non-magnetic spacer 114. Layer thicknesseswithin bi-layers 113 and 115 may range from 0.1-0.4 nm, for example.Spacer 114 provides the antiferromagnetic coupling between 113 and 115.Spacer 114 may be a Ruthenium (Ru) layer less than 1 nm thick, forexample.

Disposed over SAF stack 505 is a multi-layered filter stack 510 havinghigh temperature (HT) tolerance. As employed herein, high temperaturetolerance of the filter stack is in reference to the ability of thefilter to maintain desirable fixed magnetic layer characteristicsimpacting temperature stability and TMR of the material stack throughsubsequent thermal treatments associated with integrated circuit devicefabrication (e.g., 400° C.).

In exemplary embodiments, filter stack 510 includes at least oneferromagnetic (FM) material layer 118 disposed between a firstnon-magnetic (NM) material layer 117 and second NM material layer 119.FM material layer 118 may be of any ferromagnetic composition, such asbut not limit to Co, Fe, Ni, and alloys of these metals. In someadvantageous embodiments, FM material layer 118 is CoFeB. The CoFeBcomposition may be the same as that of fixed magnetic material layer(s)120, and/or the same as that of free magnetic material layer(s) 140. Insome CoFeB embodiments where both fixed magnetic layer(s) 120 and freemagnetic(s) 140 are Fe-rich (Fe>Co), FM material layer 118 is alsoFe-rich CoFeB, and may be 50-60% Fe. In some Fe-rich CoFeB embodiments,each of magnetic material layers 118, 120, 140 is CoFeB with 20-30% B(e.g., Co₂₀Fe₆₀B₂₀).

In accordance with some embodiments of multi-layered filter stack 510,at least one of NM material layers 117, 119 comprises a transition metalselected from the group consisting of Ta, Mo, Nb, W, and Hf. Thetransition metal may be in pure form or alloyed with other constituents.In advantageous embodiments, at least one NM material layer in filterstack 510 is predominantly (i.e., the constituent of greatest proportionin the NM material layer) one of Ta, Mo, Nb, and Hf. In someadvantageous embodiments, at least one NM material layer in filter stack510 is Ta (i.e., an NM material layer consists only of Ta).

In accordance with further embodiments, both NM material layers 117, 119comprises a transition metal selected from the group consisting of Ta,Mo, Nb, and Hf. In accordance with some such embodiments, both NMmaterial layers 117, 119 comprise the same transition metal selectedfrom the group consisting of Ta, Mo, Nb, and Hf. For example, in someembodiments both NM material layers 117 and 119 consist of Ta, orcomprise Ta in a Ta alloy of the same composition). In accordance withalternative embodiments, NM material layers 117, 119 comprise adifferent transition metal selected from the group consisting of Ta, Mo,Nb, and Hf, or comprise different alloys thereof. For example, in someembodiments a first of NM material layers 117 and 119 consists of Ta, orcomprises Ta in a first Ta alloy, while a second of NM material layers117 and 119 consists of Mo, Nb, Hf, comprises Ta in a second Ta alloy,or comprises an alloy of Mo, Nb, or Hf.

In accordance with other embodiments, only one of NM material layers117, 119 comprises a transition metal selected from the group consistingof Ta, Mo, Nb, and Hf, while the other NM material layer is an alternatemetal, such as, but not limited to W, and alloys thereof.

The thickness of the NM material layers in filter stack 510 has alsobeen found to be important with greater thicknesses permissible formaterials providing stronger magnetic coupling. In some embodiments, FMmaterial layer 118 has a thickness less than 1 nm, and for CoFeBembodiments is advantageously 0.4-0.9 nm. In some exemplary Fe-rich 20%B embodiments (e.g., Co₂₀Fe₆₀B₂₀), FM material layer 118 has a thicknessbetween 0.7 and 0.9 nm. NM material layers 117, 119 may also havethicknesses less than 1 nm, and advantageously 0.1 nm-0.5 nm. In someembodiments, thicknesses of NM material layers 117 and 119 are notequal. For example, thickness of NM material layer 119 may be thickerthan NM material layer 117 by at least 0.1 nm, with each having athickness of 0.2-0.5 nm.

Fixed magnetic material layer 120 and free magnetic material stack 155are disposed over filter stack 510. Free magnetic material stack 155includes, for example, a Mo-based metal coupling material layer havingone or more of the properties described above in the context of MTJmaterial stack 101.

FIG. 5B is a cross-sectional view of a material layer stack for a pSTTMdevice 502 further including an electrode interface material layer/stack110, in accordance with some further embodiments of the presentinvention. In the exemplary embodiment illustrated, electrode interfacematerial layer or stack 110 is disposed between electrode 107 and SAFstack 505. A seed layer 111 is further disposed between SAF stack 505and interface material layer/stack 110. The seed layer may be of amaterial having suitable composition and microstructure to promoteadvantageous crystallinity in SAF stack 505. In some embodiments, theseed layer 111 comprises Pt and may be a substantially pure Pt (i.e. notintentionally alloyed). A seed layer of Pt is well-suited as anunderlayer of a Co/Pt-based SAF structure. Electrode interface materiallayer or stack 110 is to promote an advantageous FCC structure with(111) texture in the seed layer. A Pt seed layer often deposits with FCCstructure unless strongly templated by an underlayer. The presence ofelectrode interface material layer/stack 110 is to prevent seed layerfrom templating its crystal structure based on electrode 107, such as asurface of TiN. As such, electrode interface material layer/stack 110may then be considered a crystal enhancing layer, enhancing thecrystallinity of seed layer (and SAF stack 505, etc.) relative to thecrystallinity achieved when seed layer 111 is deposited directly onelectrode 107.

In accordance with some embodiments, electrode interface material/stack110 includes at least one material layer comprising CoFeB. For example,a single CoFeB material layer may be in direct contact with both metalelectrode 107 and seed layer 111. For CoFeB electrode interfaceembodiments, seed layer 111 should be sufficiently thick to avoidmagnetic coupling to electrode interface material/stack 110. Forexemplary Pt seed layer embodiments, the Pt layer advantageously has athickness of at least 2 nm (e.g., 2-5 nm).

A CoFeB material layer 110 may have a wide range of compositions asmagnetic properties need not be optimized in the manner typical for freeand/or fixed magnetic layers. In some advantageous embodiments, CoFeBmaterial layer 110A has the same composition as that of fixed magneticmaterial layer(s) 120, and/or the same as that of free magnetic materiallayer(s) 140. CoFeB material layer 110A may have a thickness between 0.4and 5 nm.

In accordance with some further embodiments, electrode interfacematerial/stack 110 includes a CoFeB material layer in direct contactwith seed layer 111 and a Ta material layer in direct contact with metalelectrode 107. The addition of Ta material layer may improve adhesion ofCoFeB material layer to metal electrode 107 (e.g., a TiN material). TheTa material layer may have a thickness of 5 nm or less (e.g., 1-5 nm),for example.

In accordance with some further embodiments, electrode interfacematerial/stack 110 includes a Ta material layer in direct contact withseed layer 111, and a Ru material layer in direct contact with metalelectrode 107. The inventors have found Ru deposited with HCPcrystallinity promotes BCC crystallinity in a Ta material layer, whichhas further been found to favor formation of FCC crystallinity and (111)texture within seed layer 111. The Ru material layer may have athickness of 20 nm or less, and advantageously 10-20 nm.

In accordance with some further embodiments, electrode interfacematerial/stack 110 includes a Ta material layer in direct contact withthe seed layer 111 and in direct contact with metal electrode 107. Theinventors have found an elemental (pure) Ta can be employed withoutCoFeB or Ru if the Ta material layer is limited to less than 2 nm, andadvantageously 1.0-1.5 nm. The inventors have found crystallinity for Talimited to less than 1.5 nm in thickness favors formation of FCCcrystallinity and (111) texture within the seed layer.

MTJ material stacks in accordance with the architectures above may befabricated by a variety of methods applying a variety of techniques andprocessing chamber configurations. FIG. 6 is a flow diagram illustratinga method 601 for fabricating the STTM device illustrated in FIG. 1, inaccordance with some embodiments. Method 601 begins with receiving asubstrate at operation 610. Any substrate known to be suitable formicroelectronic fabrication may be received, such as, but not limited tocrystalline silicon substrates. Transistors and/or one or more levels ofinterconnect metallization may be present on the substrate as receivedat operation 610.

At operation 620, a bottom electrode metal, fixed magnetic layer ormaterial stack, and underlayers, such as a SAF structure, are deposited.At operation 630, a tunneling dielectric material, such as MgO, isdeposited directly on the fixed magnetic layer. At operation 640 a firstfree magnetic material layer, such as Fe-rich CoFeB, is depositeddirectly on the tunneling dielectric material. At operation 650, acoupling material, such as a Mo layer or Mo alloy layer, is depositeddirectly on the first free magnetic material. At operation 660, a secondfree magnetic material layer, such as Fe-rich CoFeB, is depositeddirectly on the Mo coupling material. At operation 670, a dielectric capmaterial, such as MgO, is deposited over the second free layer.Deposition of dielectric cap material is optional, and may be omittedfrom the fabrication process for a spin-hall effect implementation ofpSTTM, for example. At operation 680, a top electrode metal is depositedover the cap material. In exemplary embodiments, operations 620, 630,640, 650, 660, 670, and 680 all entail a physical vapor deposition(sputter deposition) performed at a temperature below 250° C. One ormore of co-sputter and reactive sputtering may be utilized in anycapacity known in the art to form the various layer compositionsdescribed herein. For PVD embodiments, one or more of the materiallayers, such as but not limited to the magnetic fixed and free materiallayers, are deposited in amorphous form that may be discontinuous over asubstrate area (e.g., forming islands that do not coalesce). Alternatedeposition techniques, such as atomic layer deposition (ALD) may beperformed for those materials having precursors known to be suitable.Alternatively, epitaxial processes such as, but not limited to,molecular beam epitaxy (MBE) may be practiced to grow one or more of theMTJ material layers. For one or more of these alternative depositiontechniques, at least the magnetic material layers may be deposited withat least some microstructure (e.g., polycrystalline with texture).

After one or more layers of the MTJ material stack (e.g., all layers)are deposited, an anneal is performed under any conditions known in theart to promote solid phase epitaxy of the free magnetic layers and/orfixed magnetic layer imparting polycrystalline BCC microstructure and(001) texture. Anneal temperatures, durations, and environments may varywith exemplary embodiments performing an anneal at 250° C., or more.Method 601 is completed at operation 690 where high temperature STTMand/or MOS transistor IC processing is performed, for example at atemperature of at least 400° C. Any standard microelectronic fabricationprocesses such as lithography, etch, thin film deposition, planarization(e.g., CMP), and the like may be performed to complete delineationand/or interconnection of an STTM device employing any of the MTJmaterial stacks described herein or a subset of the material layerstherein.

In an embodiment, the MTJ functions essentially as a resistor, where theresistance of an electrical path through the MTJ may exist in tworesistive states, either “high” or “low,” depending on the direction ororientation of magnetization in the free magnetic layer(s) and in thefixed magnetic layer(s). In the case that the spin direction is down(minority) in the free magnetic layer(s), a high resistive state existsand the directions of magnetization in the coupled free magneticlayer(s) and the fixed magnetic layer(s) are substantially opposed oranti-parallel with one another. In the case that the spin direction isup (majority) in the coupled free magnetic layers, a low resistive stateexists, and the directions of magnetization in the coupled free magneticlayers and the fixed magnetic layer are substantially aligned orparallel with one another. The terms “low” and “high” with regard to theresistive state of the MTJ are relative to one another. In other words,the high resistive state is merely a detectibly higher resistance thanthe low resistive state, and vice versa. Thus, with a detectibledifference in resistance, the low and high resistive states canrepresent different bits of information (i.e. a “0” or a “1”).

The direction of magnetization in the coupled free magnetic layers maybe switched through a process called spin transfer torque (“STT”) usinga spin-polarized current. An electrical current is generallynon-polarized (e.g. consisting of about 50% spin-up and about 50%spin-down electrons). A spin-polarized current is one with a greaternumber of electrons of either spin-up or spin-down. The spin-polarizedcurrent may be generated by passing a current through the fixed magneticlayer. The electrons of the spin polarized current from the fixedmagnetic layer tunnel through the tunneling barrier or dielectric layer208 and transfers its spin angular momentum to the free magnetic layer,wherein the free magnetic layer will orient its magnetic direction fromanti-parallel to that of the fixed magnetic layer or parallel. Thespin-hall effect may also be employed to generate spin-polarized currentthrough a particular electrode material that is in contact with a freemagnetic material layer. For such embodiments, the free magnetic layermay be oriented without applying current through the fixed magneticlayer and other material layers of the MTJ. In either implementation,the free magnetic layer may be returned to its original orientation byreversing the current. Thus, the MTJ may store a single bit ofinformation (“0” or “1”) by its state of magnetization. The informationstored in the MTJ is sensed by driving a current through the MTJ. Thefree magnetic layer(s) does not require power to retain its magneticorientations. As such, the state of the MTJ is preserved when power tothe device is removed. Therefore, a spin transfer torque memory bit cellcomposed of the material stacks described herein is non-volatile.

FIG. 7 is a schematic of a STTM bit cell 701, which includes a spintransfer torque element 710, in accordance with an embodiment of thepresent invention. The spin transfer torque element 710 includes a freemagnetic material stack 155 including at least two layers of magneticmaterial that are magnetically coupled through one or more interveningmetal layer comprising Mo. Element 710 further includes firstmetallization 107 proximate to fixed magnetic layer 120, and tunnelinglayer 130 disposed between free magnetic material stack 155 and fixedmagnetic layer 120, and a second metallization 180 proximate to freemagnetic material stack 155. Second metallization 180 is electricallycoupled to a first metal interconnect 792 (e.g., bit line). Firstmetallization 107 is electrically connected to a second metalinterconnect 791 (e.g., source line) through a transistor 715. Thetransistor 715 is further connected to a third metal interconnect 793(e.g., word line) in any manner conventional in the art. In SHEimplementations second metallization 180 is further coupled to a fourthmetal interconnect 794 (e.g., maintained at a reference potentialrelative to first metal interconnect 792). The spin transfer torquememory bit cell 701 may further include additional read and writecircuitry (not shown), a sense amplifier (not shown), a bit linereference (not shown), and the like, as understood by those skilled inthe art of solid state non-volatile memory devices. A plurality of thespin transfer torque memory bit cell 710 may be operably connected toone another to form a memory array (not shown), wherein the memory arraycan be incorporated into a non-volatile memory device.

FIG. 8 illustrates a system 800 in which a mobile computing platform 805and/or a data server machine 806 employs MTJ material stacks including aMo-based free magnetic coupling layer, for example in accordance withembodiments of the present invention described above. The server machine806 may be any commercial server, for example including any number ofhigh-performance computing platforms disposed within a rack andnetworked together for electronic data processing, which in theexemplary embodiment includes a packaged device 850.

The mobile computing platform 805 may be any portable device configuredfor each of electronic data display, electronic data processing,wireless electronic data transmission, or the like. For example, themobile computing platform 805 may be any of a tablet, a smart phone,laptop computer, etc., and may include a display screen (e.g., acapacitive, inductive, resistive, or optical touchscreen), a chip-levelor package-level integrated system 810, and a battery 815.

Whether disposed within the integrated system 810 illustrated in theexpanded view 820, or as a stand-alone packaged device within the servermachine 806, SOC 860 includes at least MTJ material stacks including aMo-based free magnetic coupling layer. SOC 560 may further include amemory circuitry and/or a processor circuitry 840 (e.g., STTM, MRAM, amicroprocessor, a multi-core microprocessor, graphics processor, etc.).Any of controller 835, PMIC 830, or RF (radio frequency) integratedcircuitry (RFIC) 825 may include embedded STTM employing MTJ materialstacks including a Mo-based free magnetic coupling layer.

As further illustrated, in the exemplary embodiment, RFIC 825 has anoutput coupled to an antenna (not shown) to implement any of a number ofwireless standards or protocols, including but not limited to Wi-Fi(IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, long termevolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA,TDMA, DECT, Bluetooth, derivatives thereof, as well as any otherwireless protocols that are designated as 3G, 4G, 5G, and beyond. Inalternative implementations, each of these SoC modules may be integratedonto separate ICs coupled to a package substrate, interposer, or board.

FIG. 9 is a functional block diagram of a computing device 900, arrangedin accordance with at least some implementations of the presentdisclosure. Computing device 900 may be found inside platform 905 orserver machine 906, for example. Device 900 further includes amotherboard 902 hosting a number of components, such as, but not limitedto, a processor 904 (e.g., an applications processor), which may furtherincorporate embedded magnetic memory based on MTJ material stacksincluding a Mo-based free magnetic coupling layer, in accordance withembodiments of the present invention. Processor 904 may be physicallyand/or electrically coupled to motherboard 902. In some examples,processor 904 includes an integrated circuit die packaged within theprocessor 904. In general, the term “processor” or “microprocessor” mayrefer to any device or portion of a device that processes electronicdata from registers and/or memory to transform that electronic data intoother electronic data that may be further stored in registers and/ormemory.

In various examples, one or more communication chips 906 may also bephysically and/or electrically coupled to the motherboard 902. Infurther implementations, communication chips 906 may be part ofprocessor 904. Depending on its applications, computing device 900 mayinclude other components that may or may not be physically andelectrically coupled to motherboard 902. These other components include,but are not limited to, volatile memory (e.g., DRAM), non-volatilememory (e.g., ROM), flash memory, a graphics processor, a digital signalprocessor, a crypto processor, a chipset, an antenna, touchscreendisplay, touchscreen controller, battery, audio codec, video codec,power amplifier, global positioning system (GPS) device, compass,accelerometer, gyroscope, speaker, camera, and mass storage device (suchas hard disk drive, solid-state drive (SSD), compact disk (CD), digitalversatile disk (DVD), and so forth), or the like.

Communication chips 906 may enable wireless communications for thetransfer of data to and from the computing device 900. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. Communication chips 906 may implement any ofa number of wireless standards or protocols, including but not limitedto those described elsewhere herein. As discussed, computing device 900may include a plurality of communication chips 906. For example, a firstcommunication chip may be dedicated to shorter-range wirelesscommunications, such as Wi-Fi and Bluetooth, and a second communicationchip may be dedicated to longer-range wireless communications such asGPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others.

While certain features set forth herein have been described withreference to various implementations, this description is not intendedto be construed in a limiting sense. Hence, various modifications of theimplementations described herein, as well as other implementations,which are apparent to persons skilled in the art to which the presentdisclosure pertains are deemed to lie within the spirit and scope of thepresent disclosure.

It will be recognized that the invention is not limited to theembodiments so described, but can be practiced with modification andalteration without departing from the scope of the appended claims. Forexample the above embodiments may include specific combinations offeatures as further provided below:

In one or more first embodiments, a magnetic tunneling junction (MTJ)material layer stack disposed over a substrate, the stack comprises afixed magnetic material layer or stack comprising one or more layer ofmagnetic material, a free magnetic material stack further comprising ametal coupling layer disposed between two magnetic material layers,wherein the metal coupling layer comprises at least molybdenum (Mo), anda first layer of dielectric material disposed between the fixed magneticmaterial layer or stack, and the free magnetic material layer.

In furtherance of the first embodiments, the magnetic material layershave perpendicular magnetic anisotropy, the metal coupling layer is indirect contact with each of the two magnetic material layers, and themetal coupling layer has a film thickness of 0.1 nm-1 nm.

In furtherance of the first embodiments immediately above, the metalcoupling layer is at least predominantly Mo and has a film thickness of0.1 nm-0.8 nm.

In furtherance of the first embodiments, the metal coupling layercomprises Mo alloyed with at least one of Ta, W, Nb, V, Hf, or Cr.

In furtherance of the first embodiments, the magnetic material layerseach comprise CoFeB, the first dielectric material layer comprises MgO,and the stack further comprises a synthetic antiferromagnet (SAF)structure disposed between the fixed magnetic material layer or stackand a metal electrode.

In furtherance of the first embodiments, the CoFeB layers each comprisesat least at least 50% Fe, a first of the CoFeB layers disposed betweenthe metal coupling layer and the first dielectric layer has a greaterthickness than that of a second of the CoFeB layers disposed on a sideof the metal coupling layer opposite the first of the CoFeB layers.

In furtherance of the first embodiments, the material stack furthercomprises a second layer of dielectric material disposed on a side ofthe free magnetic material stack opposite the first layer of dielectricmaterial, wherein the second layer of dielectric material comprises atleast one of: MgO, VO, TaO, HfO, ZrO, WO, or TiO.

In one or more second embodiment, a non-volatile memory cell comprises afirst electrode, a second electrode coupled to a bit line of a memoryarray, the MTJ material stack in any one of the first embodiments, and atransistor with a first terminal electrically coupled to the firstelectrode, a second terminal electrically coupled to a source line ofthe memory array, and a third terminal electrically coupled to a wordline of the memory array.

In one or more third embodiments, a non-volatile memory cell comprises afirst electrode, a second electrode coupled to a bit line of a memoryarray, and a MTJ material stack disposed between the first and secondelectrodes, wherein the MTJ material stack further comprises a fixedmagnetic material layer or stack comprising one or more layer ofmagnetic material, a free magnetic material layer comprising at leasttwo layers of magnetic material that are magnetically coupled throughone or more intervening metal coupling layer comprising molybdenum (Mo),and a dielectric layer disposed between the fixed magnetic materiallayer and the free magnetic material layer. The memory cell furthercomprises a transistor with a first terminal electrically coupled to thefirst electrode, a second terminal electrically coupled to a source lineof the memory array, and a third terminal electrically coupled to a wordline of the memory array.

In furtherance of the third embodiments, the magnetic material layershave perpendicular magnetic anisotropy, and the metal coupling layer hasa film thickness of 0.1 nm-1 nm.

In furtherance of the third embodiments immediately above, the metalcoupling layer is at least predominantly Mo and has a film thickness ofbetween 0.1 nm and 0.8 nm.

In furtherance of the third embodiments immediately above, the metalcoupling layer consists of Mo.

In furtherance of the third embodiments, the magnetic material layerseach comprise CoFeB, the first dielectric layer comprises MgO, and thefixed magnetic layer comprises a synthetic antiferromagnet (SAF).

In one or more fourth embodiments, a mobile computing platform includesa non-volatile memory comprising a plurality of the non-volatile memorycell of any of the third embodiments, a processor communicativelycoupled to the non-volatile memory, a battery coupled to the processor,and a wireless transceiver.

In one or more fifth embodiments, a method of forming a magnetictunneling junction (MTJ) material stack comprises depositing a firstlayer of a dielectric material over a substrate, depositing a firstlayer of amorphous CoFeB over the first layer of a dielectric material,depositing a metal coupling layer comprising at least molybdenum (Mo)over the first layer of amorphous CoFeB, depositing a second layer ofamorphous CoFeB over the first layer of a dielectric material,depositing a second layer of dielectric material over the second layerof CoFeB, and annealing the MTJ stack at a temperature of at least 250°C. to convert the amorphous CoFeB into polycrystalline CoFeB with <001>texture.

In furtherance of the third embodiments immediately above, depositingthe MTJ stack further comprises sputter depositing all of the layers ata temperature below 250° C.

In furtherance of the third embodiments, depositing the metal couplinglayer further comprises depositing a metal that is at leastpredominantly Mo to a film thickness of between 0.1 nm and 0.8 nm.

In furtherance of the third embodiments immediately above, depositingthe metal coupling layer further comprises depositing Mo to a filmthickness of between 0.1 nm and 0.8 nm.

In furtherance of the third embodiments, depositing the first layer ofamorphous CoFeB over the first layer of a dielectric material furthercomprises depositing the first layer of amorphous CoFeB directly on thefirst layer of a dielectric material. Depositing the metal couplinglayer comprising at least molybdenum (Mo) over the first layer ofamorphous CoFeB further comprises depositing the metal coupling layercomprising at least molybdenum (Mo) directly on the first layer ofamorphous CoFeB. Depositing the second layer of amorphous CoFeB over thefirst layer of a dielectric material further comprises depositing thesecond layer of amorphous CoFeB directly on the first layer of adielectric material. Depositing the second layer of dielectric materialover the second layer of CoFeB further comprises depositing the secondlayer of dielectric material directly on the second layer of CoFeB.

In furtherance of the third embodiments, the method further comprisingexposing the MTJ stack at a temperature of at least 400° C. duringsubsequent material processing.

However, the above embodiments are not limited in this regard and, invarious implementations, the above embodiments may include theundertaking only a subset of such features, undertaking a differentorder of such features, undertaking a different combination of suchfeatures, and/or undertaking additional features than those featuresexplicitly listed. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

1-19. (canceled)
 20. A magnetic tunneling junction (MTJ) material layerstack over a substrate, the stack comprising: a fixed magnetic materiallayer or stack comprising one or more layer of magnetic material; a freemagnetic material stack further comprising: a metal coupling layerbetween two magnetic material layers, wherein the metal coupling layercomprises at least molybdenum (Mo); and a first layer of dielectricmaterial between the free magnetic material layer and the fixed magneticmaterial layer or stack.
 21. The material stack of claim 20, wherein:the magnetic material layers have perpendicular magnetic anisotropy; themetal coupling layer is in direct contact with each of the two magneticmaterial layers; and the metal coupling layer has a film thickness of0.1 nm-1 nm.
 22. The material stack of claim 21, wherein the metalcoupling layer is at least predominantly Mo and has a film thickness of0.1 nm-0.8 nm.
 23. The material stack of claim 21, wherein the metalcoupling layer comprises Mo alloyed with at least one of Ta, W, Nb, V,Hf, or Cr.
 24. The material stack of claim 20, wherein: the magneticmaterial layers each comprise CoFeB; the first dielectric material layercomprises Mg; and the stack further comprises a syntheticantiferromagnet (SAF) structure between a metal electrode and the fixedmagnetic material layer or stack.
 25. The material stack of claim 24,wherein: the CoFeB layers each comprises at least at least 50% Fe; afirst of the CoFeB layers between the metal coupling layer and the firstdielectric layer has a greater thickness than that of a second of theCoFeB layers that is on a side of the metal coupling layer opposite thefirst of the CoFeB layers.
 26. The material stack of claim 20, furthercomprising a second layer of dielectric material on a side of the freemagnetic material stack opposite the first layer of dielectric material,wherein the second layer of dielectric material comprises an oxide of atleast one of: Mg, V, Ta, Hf, Zr, O, or Ti.
 27. A non-volatile memorycell, comprising: a first electrode; a second electrode coupled to a bitline of a memory array; the MTJ material stack of claim 1; and atransistor with a first terminal electrically coupled to the firstelectrode, a second terminal electrically coupled to a source line ofthe memory array, and a third terminal electrically coupled to a wordline of the memory array.
 28. A non-volatile memory device, comprising:a first electrode; a second electrode coupled to a bit line of a memoryarray; a MTJ material stack disposed between the first and secondelectrodes, wherein the MTJ material stack further comprises: a fixedmagnetic material layer or stack comprising one or more layer ofmagnetic material; a free magnetic material layer comprising at leasttwo layers of magnetic material that are magnetically coupled throughone or more intervening metal coupling layer comprising molybdenum (Mo);and a dielectric layer between the fixed magnetic material layer and thefree magnetic material layer; and a transistor with a first terminalelectrically coupled to the first electrode, a second terminalelectrically coupled to a source line of the memory array, and a thirdterminal electrically coupled to a word line of the memory array. 29.The memory device of claim 28, wherein: the magnetic material layershave perpendicular magnetic anisotropy; and the metal coupling layer hasa film thickness of 0.1 nm-1 nm.
 30. The memory device of claim 29,wherein the metal coupling layer is at least predominantly Mo and has afilm thickness of between 0.1 nm and 0.8 nm.
 31. The memory device ofclaim 30, wherein the metal coupling layer consists of Mo.
 32. Thememory device of claim 30, wherein: the magnetic material layers eachcomprise CoFeB; the first dielectric layer comprises Mg; and the fixedmagnetic layer comprises a synthetic antiferromagnet (SAF).
 33. A mobilecomputing platform comprising: a non-volatile memory comprising aplurality of the non-volatile memory cell of claim 27; a processorcommunicatively coupled to the non-volatile memory; a battery coupled tothe processor; and a wireless transceiver.
 34. A method of forming amagnetic tunneling junction (MTJ) material stack, comprising: depositinga first layer of a dielectric material over a substrate; depositing afirst layer of amorphous CoFeB over the first layer of a dielectricmaterial; depositing a metal coupling layer comprising at leastmolybdenum (Mo) over the first layer of amorphous CoFeB; depositing asecond layer of amorphous CoFeB over the first layer of a dielectricmaterial; depositing a second layer of dielectric material over thesecond layer of CoFeB; and annealing the MTJ stack at a temperature ofat least 250° C. to convert the amorphous CoFeB into polycrystallineCoFeB with <001> texture.
 35. The method of claim 34, wherein depositingthe MTJ stack further comprises sputter depositing all of the layers ata temperature below 250° C.
 36. The method of claim 34, whereindepositing the metal coupling layer further comprises depositing a metalthat is at least predominantly Mo to a film thickness of between 0.1 nmand 0.8 nm.
 37. The method of claim 36, wherein depositing the metalcoupling layer further comprises depositing Mo to a film thickness ofbetween 0.1 nm and 0.8 nm.
 38. The method of claim 36, wherein:depositing the first layer of amorphous CoFeB over the first layer of adielectric material further comprises depositing the first layer ofamorphous CoFeB directly on the first layer of a dielectric material;depositing the metal coupling layer comprising at least molybdenum (Mo)over the first layer of amorphous CoFeB further comprises depositing themetal coupling layer comprising at least molybdenum (Mo) directly on thefirst layer of amorphous CoFeB; depositing the second layer of amorphousCoFeB over the first layer of a dielectric material further comprisesdepositing the second layer of amorphous CoFeB directly on the firstlayer of a dielectric material; and depositing the second layer ofdielectric material over the second layer of CoFeB further comprisesdepositing the second layer of dielectric material directly on thesecond layer of CoFeB.
 39. The method of claim 34, further comprisingexposing the MTJ stack at a temperature of at least 400° C. duringsubsequent material processing.